staging: comedi: comedi_test: simplify time since last AI scan

The private data structure `struct waveform_private` currently uses
member `last` to remember the time of the last timer interrupt, and the
member `usec_remainder` to keep track of how far into a simulated scan
the interrupt occurred.  Replace these with a single new member
`ai_last_scan_time` that records the time of the last scan.  This
simplifies the calculation of the number of scans to simulate in the
timer routine, `waveform_ai_interrupt()`.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>
Reviewed-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/staging/comedi/drivers/comedi_test.c b/drivers/staging/comedi/drivers/comedi_test.c
index 158e090..78fde3a 100644 (file)
--- a/drivers/staging/comedi/drivers/comedi_test.c
+++ b/drivers/staging/comedi/drivers/comedi_test.c
@@ -62,11 +62,10 @@ enum waveform_state_bits {
 /* Data unique to this driver */
 struct waveform_private {
        struct timer_list timer;
-       ktime_t last;   /* time last timer interrupt occurred */
+       u64 ai_last_scan_time;          /* time of last AI scan in usec */
        unsigned int uvolt_amplitude;   /* waveform amplitude in microvolts */
        unsigned int usec_period;       /* waveform period in microseconds */
        unsigned int usec_current;      /* current time (mod waveform period) */
-       unsigned long usec_remainder;   /* usec since last scan */
        unsigned long state_bits;
        unsigned int scan_period;       /* scan period in usec */
        unsigned int convert_period;    /* conversion period in usec */
@@ -184,27 +183,19 @@ static void waveform_ai_interrupt(unsigned long arg)
        struct comedi_async *async = s->async;
        struct comedi_cmd *cmd = &async->cmd;
        unsigned int i, j;
-       /* all times in microsec */
        unsigned long elapsed_time;
        unsigned int num_scans;
-       ktime_t now;
 
        /* check command is still active */
        if (!test_bit(WAVEFORM_AI_RUNNING, &devpriv->state_bits))
                return;
 
-       now = ktime_get();
-
-       elapsed_time = ktime_to_us(ktime_sub(now, devpriv->last));
-       devpriv->last = now;
-       num_scans =
-           (devpriv->usec_remainder + elapsed_time) / devpriv->scan_period;
-       devpriv->usec_remainder =
-           (devpriv->usec_remainder + elapsed_time) % devpriv->scan_period;
+       elapsed_time = ktime_to_us(ktime_get()) - devpriv->ai_last_scan_time;
+       num_scans = elapsed_time / devpriv->scan_period;
 
        num_scans = comedi_nscans_left(s, num_scans);
        for (i = 0; i < num_scans; i++) {
-               unsigned long scan_remain_period = devpriv->scan_period;
+               unsigned int scan_remain_period = devpriv->scan_period;
 
                for (j = 0; j < cmd->chanlist_len; j++) {
                        unsigned short sample;
@@ -219,6 +210,7 @@ static void waveform_ai_interrupt(unsigned long arg)
                        scan_remain_period -= devpriv->convert_period;
                }
                devpriv->usec_current += scan_remain_period;
+               devpriv->ai_last_scan_time += devpriv->scan_period;
        }
        if (devpriv->usec_current >= devpriv->usec_period)
                devpriv->usec_current %= devpriv->usec_period;
@@ -337,6 +329,7 @@ static int waveform_ai_cmd(struct comedi_device *dev,
 {
        struct waveform_private *devpriv = dev->private;
        struct comedi_cmd *cmd = &s->async->cmd;
+       u64 usec_current;
 
        if (cmd->flags & CMDF_PRIORITY) {
                dev_err(dev->class_dev,
@@ -356,10 +349,10 @@ static int waveform_ai_cmd(struct comedi_device *dev,
                devpriv->scan_period = cmd->scan_begin_arg / NSEC_PER_USEC;
        }
 
-       devpriv->last = ktime_get();
-       devpriv->usec_current =
-               ((u32)ktime_to_us(devpriv->last)) % devpriv->usec_period;
-       devpriv->usec_remainder = 0;
+       devpriv->ai_last_scan_time = ktime_to_us(ktime_get());
+       /* Determine time within waveform period. */
+       usec_current = devpriv->ai_last_scan_time;
+       devpriv->usec_current = do_div(usec_current, devpriv->usec_period);
 
        devpriv->timer.expires = jiffies + 1;
        /* mark command as active */